Polycarbonate comprising different kinds of bonding units and process for the preparation thereof

ABSTRACT

Disclosed is a polycarbonate comprising a plurality of aromatic polycarbonate main chains, wherein the aromatic polycarbonate main chains collectively contain specific heterounits in a specific amount in the polycarbonate main chains. The polycarbonate of the present invention can be obtained by controlling the temperature of and the residence time of the polymerizable material in the reaction zones of the reaction system so as to satisfy the specific requirements. The polycarbonate of the present invention is advantageous in that not only does it have high transparency and colorlessness as well as high mechanical strength, but also it can exhibit high non-Newtonian flow properties, so that it exhibits high molding melt fluidity. Therefore, the polycarbonate of the present invention is extremely advantageous from a commercial point of view.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polycarbonate having heterounits anda method for producing the same. More particularly, the presentinvention is concerned with a polycarbonate comprising a plurality ofaromatic polycarbonate main chains, wherein the aromatic polycarbonatemain chains collectively contain specific heterounits in a specificamount in the polycarbonate main chains, and a method for producing thesame. The polycarbonate of the present invention is advantageous in thatnot only does it have high transparency and colorlessness as well ashigh mechanical strength, but also it can exhibit high non-Newtonianflow properties, so that it exhibits high molding melt fluidity.Therefore, the polycarbonate of the present invention is extremelyadvantageous from a commercial point of view.

2. Prior Art

Polycarbonates have been widely used in various fields as engineeringplastics having excellent heat resistance, impact resistance andtransparency. Production of polycarbonates has conventionally beenconducted by using the phosgene process. However, polycarbonatesproduced by using the phosgene process have problems in that theproduction thereof needs the use of phosgene, which is poisonous, andthat they contain residual methylene chloride (solvent), which not onlyadversely affects the thermal stability of the polycarbonates, but alsocauses corrosion of a mold used for the molding of the polycarbonates.Therefore, recently, polycarbonates produced by using thetransesterification process have been drawing attention.

With respect to transesterification polycarbonates, it is known: thatalmost colorless, transparent transesterification can be obtained on alaboratory scale; however, when the production of transesterificationpolycarbonates is conducted on a commercial scale, only those havingslightly yellowish color can be obtained [see “Purasuchikku Zairyo Koza(5), Porikaboneto Jushi (Lecture on Plastic Materials (5), PolycarbonateResins)”, page 66, published in 1981 by The Nikkan Kogyo Shimbun Ltd.,Japan], and that transesterification polycarbonates have disadvantagesin that they have many branched structures, so that they have poorstrength (danger of brittle fracture is high), as compared to phosgeneprocess polycarbonates [see “Kobunshi (Polymer)”, vol. 27, p. 521, July1978)].

In order to alleviate these problems of the transesterificationpolycarbonates, various studies have been made on the structure andproduction process of the transesterification polycarbonates. Withrespect to the branched structures of the transesterificationpolycarbonates, it is known that such branched structures are formed asfollows. During the progress of the polymerization reaction in thepresence of an alkali in the reaction system, the polycarbonate chainbeing formed suffers a side reaction represented by the reaction formuladescribed below, which is similar to the Kolbe-Schmitt reaction:

As is apparent from the above-shown structure formed in the main chainby the side reaction, a branched chain grows and extends through esterbonds. In some cases, such a branched chain forms a crosslinkedstructure in the final polycarbonate [see “Purasuchikku Zairyo Koza (5),Porikaboneto Jushi (Lecture on Plastic Materials (5), PolycarbonateResins)”, page 64, published in 1981 by The Nikkan Kogyo Shimbun Ltd.,Japan; and “Porikaboneto Jushi Hando Bukku (Polycarbonate Resin HandBook)”, page 49, published in 1992 by The Nikkan Kogyo Shimbun Ltd.,Japan].

With respect to the structure of the transesterification polycarbonate,it has been attempted to reduce the amount of branched structure in thepolycarbonate. For example, Unexamined Japanese Patent ApplicationLaid-Open Specification No. 5-105751 and Unexamined Japanese PatentApplication Laid-Open Specification No. 5-202180 (corresponding to U.S.Pat. No. 5,468,836) disclose a technique to obtain a transesterificationpolycarbonate having no or an extremely small amount of branchedstructure. Specifically, in these prior art documents, thetransesterification reaction is conducted using a specific combinationof catalysts, to thereby obtain a colorless, transparent polycarbonatehaving no or an extremely small amount of branched structure which isformed by the side reaction during the polymerization. UnexaminedJapanese Patent Application Laid-Open Specification No. 7-18069(corresponding to U.S. Pat. No. 5,418,316) proposes a method forproducing a polycarbonate, in which, by the use of a specific catalyst,the amount of the above-mentioned branched structure formed by the sidereaction similar to the Kolbe-Schmitt reaction is suppressed to a levelas low as 300 ppm or less. The polycarbonates disclosed in these priorart documents have high transparency and colorlessness; however, thesepolycarbonates have problems in that they exhibit poor non-Newtonianflow properties, so that they disadvantageously exhibit low molding meltfluidity.

For solving the above problems, for example, Unexamined Japanese PatentApplication Laid-Open Specification Nos. 5-271400 and 5-295101 (eachcorresponding to U.S. Pat. No. 5,468,836) disclose a transesterificationtechnique in which the formation of the above-mentioned disadvantageousbranched structure resulting from the side reaction of the abovereaction formula is reduced by the use of a specific catalyst to therebyachieve an improvement in transparency and colorlessness of the formedpolycarbonate, whereas the non-Newtonian flow properties of thepolycarbonate are improved by intentionally introducing another specificbranched structure to the polycarbonate by the use of a multifunctionalcompound, to thereby improve the properties of the polycarbonate so thatit can be advantageously used for blow molding. Further, in U.S. Pat.No. 4,562,242, it is attempted to improve the molding melt fluidity ofthe polycarbonate by the use of a 5-(dimethyl-p-hydroxybenzyl) salicylicacid as a branching agent. However, the use of the multifunctionalcompounds as mentioned above has problems in that these compoundspromote a crosslinking reaction during the polymerization, so that thefinal polycarbonate is likely to contain gel.

Therefore, it has been desired to develop a transesterificationtechnique, in which the occurrence of branching of the polycarbonatestructure can be controlled without using a multifunctional compoundwhich is likely to cause gelation, so as to produce a polycarbonatewhich not only has high transparency and colorlessness as well as highmechanical strength, but also exhibits high non-Newtonian flowproperties, so that the polycarbonate can exhibit high molding meltfluidity, as compared to the phosgene process polycarbonates.

Further, with respect to the process for producing a transesterificationpolycarbonate, various improvements have been proposed. For example,with respect to a process in which use is made of a plurality ofpolymerizers which are connected in series, it has been proposed to usea special type of polymerizer as a final stage polymerizer, such as aspecial type of horizontal agitation type polymerizer (see UnexaminedJapanese Patent Application Laid-Open Specification No. 2-153923) or atwin screw vented extruder (see Examined Japanese Patent ApplicationPublication No. 52-36159 and Unexamined Japanese Patent ApplicationLaid-Open Specification No. 63-23926. However, the techniques of theabove-mentioned prior art documents are only intended to promote theremoval of phenol from the polymerization reaction system. Therefore, bythese techniques, a polycarbonate having a high molecular weight can beeasily obtained; however, the obtained polycarbonate is not satisfactorywith respect to the properties thereof, such as mechanical propertiesand molding melt fluidity.

The task of the present invention is to provide a polycarbonate which isadvantageous in that not only does it have high transparency andcolorlessness as well as high mechanical strength, but also it exhibitshigh non-Newtonian flow properties, so that it can exhibit high moldingmelt fluidity.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward solving the above-mentionedproblems accompanying the conventional polycarbonates. As a result, ithas been found that a polycarbonate comprising a plurality of aromaticpolycarbonate main chains, wherein the aromatic polycarbonate mainchains collectively contain specific heterounits in a specific amount inthe polycarbonate chains, is free from the above-mentioned problemsaccompanying the conventional polycarbonates, and is advantageous inthat not only does it have high transparency and colorlessness as wellas high mechanical strength, but also it exhibits high non-Newtonianflow properties, so that it can exhibit high molding melt fluidity.

Accordingly, it is an object of the present invention to provide apolycarbonate which is advantageous in that not only does it have hightransparency and colorlessness as well as high mechanical strength, butalso it exhibits high non-Newtonian flow properties, so that it canexhibit high molding melt fluidity.

It is another object of the present invention to provide a method forproducing the above-mentioned excellent polycarbonate.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims taken in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 is a diagram showing the system employed for producing apolycarbonate in Example 1.

DESCRIPTION OF REFERENCE NUMERALS

(FIG. 1)

1A-6A: Numerals assigned in connection with first vertical agitationtype polymerizer vessel (A)

1B-6B: Numerals assigned in connection with first vertical agitationtype polymerizer vessel (B)

1C-7C: Numerals assigned in connection with second vertical agitationtype polymerizer vessel (C)

1D-7D: Numerals assigned in connection with third vertical agitationtype polymerizer vessel (D)

101A-109A: Numerals assigned in connection with first wire-wetting fallpolymerizer

101B-109B: Numerals assigned in connection with second wire-wetting fallpolymerizer

1A, 1B: Inlet for a starting polymerizable material

1C, 1D: Inlet for a prepolymer

2A, 2B, 2C, 2D: Vent

3A, 3B: First vertical agitation type polymerizer vessels (A) and (B)

3C: Second vertical agitation type polymerizer vessel (C)

3D: Third vertical agitation type polymerizer vessel (D)

4A, 4B, 4C, 4D: Molten prepolymer

5A, 5B, 5C, 5D: Outlet

6A, 6B, 6C, 6D: Agitator

7C, 7D, 8: Transfer pump

101A, 101B: Inlet for a prepolymer

102A, 102B: Perforated plate

103A, 103B: Wire

104A, 104B: Gas feed port

105A, 105B: Vent

106A: Transfer pump

106B: Discharge pump

107A, 107B: Outlet

108A, 108B: Main body of wire-wetting fall polymerizer

109A: Molten Prepolymer

109B: Molten Polymer

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a polycarbonatecomprising a plurality of aromatic polycarbonate main chains, eachcomprising recurring units each independently represented by thefollowing formula (1):

wherein Ar represents a divalent C₅-C₂₀₀ aromatic group,

wherein the plurality of aromatic polycarbonate main chains collectivelycontain at least one heterounit (A) and at least one heterounit (B) inthe polycarbonate main chains,

the heterounit (A) being represented by a formula selected from thefollowing group (2) of formulae:

wherein Ar′ represents a trivalent C₅-C₂₀₀ aromatic group, Ar″represents a tetravalent C₅-C₂₀₀ aromatic group, and X represents apolycarbonate chain having recurring units each represented by theformula

wherein Ar is as defined above and having a weight average molecularweight of from 214 to 100,000, and

wherein, when the polycarbonate main chains contain a plurality ofheterounits (A), the heterounits (A) are the same or different,

the heterounit (B) being represented by a formula selected from thefollowing group (3) of formulae:

wherein Ar, Ar′ and X are as defined above and Y represents apolycarbonate chain having recurring units each represented by theformula

wherein Ar is as defined above and having a weight average molecularweight of from 214 to 100,000, and

wherein, when the polycarbonate main chains contain a plurality ofheterounits (B), the heterounits (B) are the same or different,

the sum of the amounts of the heterounit (A) and the heterounit (B)being from 0.01 to 0.3 mole %, based on the molar amount of therecurring units (1),

wherein each of X and Y optionally contains at least one heterounitselected from the group consisting of heterounits (A) and (B),

the polycarbonate having a weight average molecular weight of from 5,000to 300,000.

For easy understanding of the present invention, the essential featuresand various embodiments of the present invention are enumerated below.

1. A polycarbonate comprising a plurality of aromatic polycarbonate mainchains, each comprising recurring units each independently representedby the following formula (1):

wherein Ar represents a divalent C₅-C₂₀₀ aromatic group, wherein theplurality of aromatic polycarbonate main chains collectively contain atleast one heterounit (A) and at least one heterounit (B) in thepolycarbonate main chains,

the heterounit (A) being represented by a formula selected from thefollowing group (2) of formulae:

wherein Ar′ represents a trivalent C₅-C₂₀₀ aromatic group, Ar″represents a tetravalent C₅-C₂₀₀ aromatic group, and X represents apolycarbonate chain having recurring units each represented by theformula

wherein Ar is as defined above and having a weight average molecularweight of from 214 to 100,000, and

wherein, when the polycarbonate main chains contain a plurality ofheterounits (A), the heterounits (A) are the same or different,

the heterounit (B) being represented by a formula selected from thefollowing group (3) of formulae:

wherein Ar, Ar′ and X are as defined above and Y represents apolycarbonate chain having recurring units each represented by theformula

and having a weight average molecular weight of from 214 to 100,000, and

wherein, when the polycarbonate main chains contain a plurality ofheterounits (B), the heterounits (B) are the same or different,

the sum of the amounts of the heterounit (A) and the heterounit (B)being from 0.01 to 0.3 mole %, based on the molar amount of therecurring units (1),

wherein each of X and Y optionally contains at least one heterounitselected from the group consisting of heterounits (A) and (B),

the polycarbonate having a weight average molecular weight of from 5,000to 300,000.

2. The polycarbonate according to item 1 above, wherein 85% or more ofthe recurring units (1) are each represented by the following formula(1′):

3. The polycarbonate according to item 1 above, wherein:

the recurring units (1) are each represented by the following formula(1′):

the heterounit (A) is represented by a formula selected from thefollowing group (2′) of formulae:

wherein X is as defined for formula (2), and

the heterounit (B) is represented by a formula selected from thefollowing group (3′) of formulae:

wherein X is as defined for formula (2), and Y is as defined for formula(3).

4. The polycarbonate according to any one of items 1 to 3 above, whereinthe heterounit (B) is present in an amount of from 0.1 to 30 mole %,based on the molar amount of the heterounit (A).

5. The polycarbonate according to any one of items 1 to 4 above, whichis produced from an aromatic dihydroxy compound and a carbonic diesterby transesterification.

6. In a method for producing a polycarbonate which comprises subjectingto a stepwise transesterification reaction, in a plurality of reactionzones, at least one polymerizable material selected from the groupconsisting of:

a molten monomer mixture of an aromatic dihydroxy compound and acarbonic diester, and

a molten prepolymer obtained by a process comprising reacting anaromatic dihydroxy compound with a carbonic diester,

the aromatic dihydroxy compound being represented by the followingformula:

HO—Ar—OH

wherein Ar represents a divalent C₅-C₂₀₀ aromatic group,

the carbonic diester being represented by the following formula:

wherein Ar³ and Ar⁴ are the same or different and each represent amonovalent C₅-C₂₀₀ aromatic group,

the improvement in which the stepwise transesterification reaction ofthe polymerizable material is performed under reaction conditions whichsatisfy the following formula (4): $\begin{matrix}{0.2 \leqq {\sum\limits_{i = 1}^{n}\quad \left( {{ki} \times {Ti} \times {Hi}} \right)} \leqq 1.2} & (4)\end{matrix}$

wherein:

i represents the zone number assigned in an arbitrary order among nreaction zones of the reaction system,

Ti represents the average temperature (°C.) of the polymerizablematerial in the i-th reaction zone, Hi represents the average residencetime (hr) of the polymerizable material in the i-th reaction zone,

ki represents a coefficient represented by the following formula (5):

ki=1/(a×Ti^(-b))   (5)

wherein Ti is as defined above, and a and b depend on Ti, and wherein:

when Ti satisfies the formula:

Ti<240° C.,

a is 1.60046×10⁵ and b is 0.472,

when Ti satisfies the formula:

240° C.≦Ti<260° C.,

a is 4×10⁴⁹ and b is 19.107, and

when Ti satisfies the formula:

260° C.≦Ti,

a is 1×10¹²² and b is 49.082.

7. A polycarbonate which is substantially the same product as producedby the method of item 6 above.

The polycarbonate of the present invention comprises a plurality ofaromatic polycarbonate chains, each comprising recurring units eachindependently represented by the formula (1) above, wherein the aromaticpolycarbonate chains collectively contain at least one heterounit (A)and at least one heterounit (B). The heterounit (A) is represented by aformula selected from the above-mentioned formulae of group (2). Whenthe aromatic polycarbonate chains contain a plurality of the heterounits(A), the heterounits (A) may be the same or different. The heterounit(B) is represented by a formula selected from the above-mentionedformulae of group (3). When the aromatic polycarbonate chains contain aplurality of the heterounits (B), the heterounits (B) may be the same ordifferent.

In the formula (1), the formulae of group (2) and the formulae of group(3), each Ar independently represents a divalent C₅-C₂₀₀ aromatic group,each Ar′ independently represents a trivalent C₅-C₂₀₀ aromatic groupwhich has a structure equivalent to a mono-substituted Ar, and each Ar″independently represents a tetravalent C₅-C₂₀₀ aromatic group which hasa structure equivalent to a di-substituted Ar. Examples of divalentaromatic groups Ar include phenylene, naphthylene, biphenylene,pyridylene and a divalent aromatic group represented by the formula:—Ar¹—Q—Ar²—, wherein each of Ar¹ and Ar² independently represents adivalent C₅-C₇₀ carbocyclic or heterocyclic aromatic group, and Qrepresents a divalent C₁-C₃₀ alkane group.

In the divalent aromatic groups Ar¹ and Ar², at least one hydrogen atommay be replaced by a substituent which does not adversely affect thereaction, such as a halogen atom, an alkyl group having from 1 to 10carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a phenylgroup, a phenoxy group, a vinyl group, a cyano group, an ester group, anamide group or a nitro group.

Specific examples of heterocyclic aromatic groups include an aromaticgroup having in a skeleton thereof at least one hetero atom, such as anitrogen atom, an oxygen atom or a sulfur atom.

Examples of divalent aromatic groups Ar¹ and Ar² include anunsubstituted or substituted phenylene group, an unsubstituted orsubstituted biphenylene group and an unsubstituted or substitutedpyridylene group. Substituents for Ar¹ and Ar² are as described above.

Examples of divalent alkane groups Q include organic groups respectivelyrepresented by the following formulae:

wherein each of R¹, R², R³ and R⁴ independently represents a hydrogenatom, an alkyl group having from 1 to 10 carbon atoms, an alkoxy grouphaving from 1 to 10 carbon atoms, a cycloalkyl group having from 5 to 10ring-forming carbon atoms, a carbocyclic aromatic group having from 5 to10 ring-forming carbon atoms or a carbocyclic aralkyl group having from6 to 10 ring-forming carbon atoms; k represents an integer of from 3 to11; each Z represents a carbon atom and has R⁵ and R⁶ bonded thereto;each R⁵ independently represents a hydrogen atom or an alkyl grouphaving from 1 to 6 carbon atoms, and each R⁶ independently represents ahydrogen atom or an alkyl group having from 1 to 6 carbon atoms; and

wherein at least one hydrogen atom of each of R¹, R², R³, R⁴, R⁵ and R⁶may be independently replaced by a substituent which does not adverselyaffect the reaction, such as a halogen atom, an alkyl group having from1 to 10 carbon atoms, an alkoxy group having from 1 to 10 carbon atoms,a phenyl group, a phenoxy group, a vinyl group, a cyano group, an estergroup, an amide group or a nitro group.

Specific examples of divalent aromatic groups Ar include groupsrespectively represented by the following formulae:

wherein each of R⁷ and R⁸ independently represents a hydrogen atom, ahalogen atom, an alkyl group having from 1 to 10 carbon atoms, an alkoxygroup having from 1 to 10 carbon atoms, a cycloalkyl group having from 5to 10 ring-forming carbon atoms, or an phenyl group; each of m and nindependently represents an integer of from 1 to 4, with the provisothat when m is an integer of from 2 to 4, the R⁷ s are the same ordifferent, and when n is an integer of from 2 to 4, the R⁸'s are thesame or different.

Further examples of divalent aromatic groups Ar include those which arerepresented by the following formula:

—Ar¹—Z′—Ar²—

wherein Ar¹ and Ar² are as defined above; and Z′ represents a singlebond or a divalent group, such as —O—, —CO—, —S—, —SO₂, —SO—, —COO—, or—CON(R¹)—, wherein R¹ is as defined above.

Examples of such divalent aromatic groups Ar include groups respectivelyrepresented by the following formulae:

wherein R⁷, R⁸, m and n are as defined above.

In the present invention, these aromatic groups Ar may be usedindividually or in combination. As a preferred example of recurringunits of the formula (1) in the polycarbonate of the present invention,there can be mentioned a unit represented by the above-mentioned formula(1′), which is derived from bisphenol A. It is preferred that 85 mole %or more of the recurring units (1) are the units of the formula (1′).

With respect to the heterounit (A), it is preferred that the heterounit(A) is one which is represented by a formula selected from the formulaeof the following group (2′) of formulae:

wherein X is as defined for formula (2).

In the polycarbonate of the present invention, it is necessary that thearomatic polycarbonate chains collectively contain at least oneheterounit (A).

With respect to the heterounit (B), it is preferred that the heterounit(B) is one which is represented by a formula selected from the followinggroup (3′) of formulae:

wherein X is as defined for formula (2), and

Y is as defined for formula (3).

In the polycarbonate of the present invention, it is necessary that thearomatic polycarbonate chains collectively contain at least oneheterounit (B).

In the polycarbonate of the present invention, it is necessary that thesum of the amounts of the heterounit (A) and the heterounit (B) be inthe range of from 0.01 to 0.3 mole %, based on the molar amount of therecurring units (1).

When the sum of the amounts of the heterounit (A) and the heterounit (B)is less than 0.01 mole %, the non-Newtonian flow properties of thepolycarbonate lowers, so that the molding melt fluidity, (i.e., thefluidity of the polycarbonate at a high shear rate) is caused to lower.When the sum of the amounts of the heterounit (A) and the heterounit (B)is more than 0.3 mole %, the mechanical properties (such as tensileelongation and Izod impact strength) of the polycarbonate lower.

In the present invention, the sum of the heterounit (A) and theheterounit (B) is preferably in the range of from 0.02 to 0.25 mole %,more preferably from 0.03 to 0.2 mole %, based on the molar amount ofthe recurring units (1). In the present invention, for achieving a goodbalance of the molding melt fluidity and the mechanical strength, it ispreferred that the polycarbonate contains the heterounit (B) in anamount of from 0.1 to 30 mole %, more preferably from 0.1 to 10 mole %,based on the molar amount of the heterounit (A).

In the present invention, the determination of each of the recurringunits (1), and the heterounits (A) and (B) can be conducted, forexample, by a method in which the polycarbonate is completelyhydrolyzed, and the resultant hydrolysis mixture is analyzed by reversedphase liquid chromatography (the analysis by reversed phase liquidchromatography can be conducted under the conditions as described belowin the Examples). With respect to the hydrolysis of the polycarbonate,it is preferred that the hydrolysis be conducted at room temperature bythe method described in Polymer Degradation and Stability 45 (1994),127-137. The hydrolysis by this method is advantageous in that thecomplete hydrolysis of a polycarbonate can be achieved by simpleoperation, wherein it is free from the danger of occurrence of sidereactions during the hydrolysis.

The polycarbonate of the present invention has a weight averagemolecular weight of from 5,000 to 300,000. When the weight averagemolecular weight is lower than 5,000, the mechanical strength of thepolycarbonate lowers. When the weight average molecular weight is higherthan 300,000, the molding melt fluidity of the polycarbonate lowers. Inthe present invention, the weight average molecular weight of thepolycarbonate is preferably from 7,000 to 100,000, more preferably from10,000 to 80,000.

In the present invention, the terminal structure of the polycarbonate isnot particularity limited. The terminal group of the polycarbonate maybe at least one group selected from a hydroxyl group, an aryl carbonategroup and an alkyl carbonate group. The above-mentioned terminalhydroxyl group is derived from the aromatic dihydroxy compound used inthe polymerizable material.

The terminal aryl carbonate group is represented by the followingformula:

wherein Ar³ represents an unsubstituted or

substituted monovalent C₆-C₃₀ aromatic group.

Specific examples of terminal aryl carbonate groups include groupsrespectively represented by the following formulae:

The terminal alkyl carbonate group is represented by the followingformula:

wherein R⁷ represents a straight chain or branched alkyl group having 1to 20 carbon atoms.

Specific examples of terminal alkyl carbonate groups include groupsrespectively represented by the following formulae:

Among these terminal groups, a phenyl carbonate group, a p-t-butylphenylcarbonate group and a p-cumylphenyl carbonate group are preferred. Withrespect to the molar ratio of the terminal hydroxyl group to otherterminal groups, there is no particular limitation. However, the molarratio is generally selected in the range of from 0:100 to 100:0depending on the use. From the viewpoint of improving heat resistanceand hot water resistance, it is preferred that the amount of theterminal hydroxy group be as small as possible.

Hereinbelow, the method of the present invention for producing apolycarbonate is explained.

The method of the present invention comprises subjecting to a stepwisetransesterification reaction, in a plurality of reaction zones, at leastone polymerizable material selected from the group consisting of:

a molten monomer mixture of an aromatic dihydroxy compound and acarbonic diester, and

a molten prepolymer obtained by a process comprising reacting anaromatic dihydroxy compound with a carbonic diester,

the aromatic dihydroxy compound being represented by the followingformula:

HO—Ar—OH

wherein Ar represents a divalent C₅-C₂₀₀ aromatic group,

the carbonic diester being represented by the following formula:

wherein Ar³ and Ar⁴ are the same or different and each represent amonovalent C₅-C₂₀₀ aromatic group,

wherein the stepwise transesterification reaction of the polymerizablematerial is performed under reaction conditions which satisfy thefollowing formula (4): $\begin{matrix}{0.2 \leqq {\sum\limits_{i = 1}^{n}\quad \left( {{ki} \times {Ti} \times {Hi}} \right)} \leqq 1.2} & (4)\end{matrix}$

wherein:

i represents the zone number assigned in an arbitrary order among nreaction zones of the reaction system,

Ti represents the average temperature (° C.) of the polymerizablematerial in the i-th reaction zone,

Hi represents the average residence time (hr) of the polymerizablematerial in the i-th reaction zone,

ki represents a coefficient represented by the following formula (5):

ki=1/(a×Ti^(-b))   (5)

wherein Ti is as defined above, and

a and b depend on Ti, and wherein:

when Ti satisfies the formula:

Ti<240° C.,

a is 1.60046×10⁵ and b is 0.472,

when Ti satisfies the formula:

240° C.≦Ti<260° C.,

a is 4×10⁴⁹ and b is 19.107, and

when Ti satisfies the formula:

260° C.≦Ti,

a is 1×10¹²² and b is 49.082.

In the present invention, the term “aromatic dihydroxy compound” means acompound represented by the formula: HO—Ar—OH wherein Ar is as definedabove. In the present invention, the aromatic dihydroxy compound may bea single type of aromatic dihydroxy compound or a combination of 2 ormore types of aromatic dihydroxy compounds. It is preferred to use anaromatic dihydroxy compound in which the contents of a chlorine atom, analkali metal and an alkaline earth metal are low. It is more preferredto use an aromatic dihydroxy compound substantially free from a chlorineatom, an alkali metal and an alkaline earth metal.

The carbonic diester used in the present invention is represented by thefollowing formula:

wherein Ar³ and Ar⁴ are the same or different and each represent amonovalent C₅-C₂₀₀ aromatic group.

In each of Ar³ and Ar⁴, which independently represents a monovalentcarbocyclic or heterocyclic aromatic group, at least one hydrogen atommay be replaced by a substituent which does not adversely affect thereaction, such as a halogen atom, an alkyl group having from 1 to 10carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a phenylgroup, a phenoxy group, a vinyl group, a cyano group, an ester group, anamide group or a nitro group. Ar³ and Ar⁴ may be the same or different.

Representative examples of monovalent aromatic groups Ar³ and Ar⁴include a phenyl group, a naphthyl group, a biphenyl group and a pyridylgroup. These groups may or may not be substituted with theabove-mentioned substitutent or substituents.

Preferred examples of monovalent aromatic groups as Ar³ and Ar⁴ includethose which are respectively represented by the following formulae:

Representative examples of carbonic diesters include di(unsubstituted orsubstituted)phenyl carbonate compounds represented by the followingformula:

wherein each of R⁹ and R¹⁰ independently represents a hydrogen atom, analkyl group having from 1 to 10 carbon atoms, an alkoxy group havingfrom 1 to 10 carbon atoms, a cycloalkyl group having from 5 to 10ring-forming carbon atoms or a phenyl group; each of p and qindependently represents an integer of from 1 to 5, with the provisothat when p is an integer of 2 or more, the R⁹'s are the same ordifferent, and when q is an integer of from 2 or more, the R¹⁰'s are thesame or different.

Of these diphenyl carbonate compounds, preferred are those having asymmetrical configuration, for example di(unsubstituted)phenyl carbonateand di(lower alkyl-substituted)phenyl carbonates, e.g., ditolylcarbonate and di-t-butylphenyl carbonate. Particularly preferred isdiphenyl carbonate which has the simplest structure.

These carbonic diesters may be used individually or in combination. Itis preferred that these carbonic diesters have a low content of achlorine atom, an alkali metal or an alkaline earth metal. It is mostpreferred that these carbonic diesters are substantially free from achlorine atom, an alkali metal and an alkaline earth metal.

The ratio in which the aromatic dihydroxy compound and the carbonicdiester are used (i.e., a charging ratio) may be varied depending on thetypes of the aromatic dihydroxy compound and carbonic diester employed,the polymerization temperature and other polymerization conditions, andthe desired molecular weight of a polycarbonate to be obtained and thedesired proportions of the terminal groups in the polycarbonate. Thecarbonic diester is generally used in an amount of from 0.9 to 2.5moles, preferably from 0.95 to 2.0 moles, more preferably from 0.98 to1.5 moles, per mole of the aromatic dihydroxy compound.

In the present invention, the heterounit (A) and the heterounit (B) areformed during the polymerization reaction, so that the finalpolycarbonate contains the heterounit (A) and the heterounit (B).

In the present invention, for the purpose of introducing a branchedstructure to the polycarbonate, an aromatic poly(tri or more)hydroxycompound may be used in a small amount in the production of thepolycarbonate, as long as the polycarbonate satisfying theabove-mentioned requirements of the present invention can be obtained.Also, an aromatic monohydroxy compound or an aliphatic alcohol may beused for changing the terminal groups, or adjusting the molecular weightof the polycarbonate.

In the present invention, the production of a polycarbonate is conductedby a transesterification process which is a process wherein acondensation polymerization of the polymerizable material is performedby transesterification in the molten state or solid state while heatingin the presence or absence of a catalyst under reduced pressure, underan inert gas flow or under both reduced pressure and an inert gas flow.The mode of the transesterification process, the polymerizationequipment and the like are not specifically limited. For example, when amolten-state transesterification is employed, examples of reactorsemployable for performing the transesterification reaction include anagitation type reactor vessel, a wiped film type reactor, a centrifugalwiped film evaporation type reactor, a surface renewal type twin-screwkneading reactor, a twin-screw horizontal agitation type reactor, awall-wetting fall reactor, a free-fall polymerizer having a perforatedplate, and a wire-wetting fall polymerizer having a perforated plate andat least one wire provided in association with the perforated plate.These various types of reactors can be used individually or incombination. Further, for example, the transesterification reaction canalso be performed by a method in which a molten-statetransesterification is first conducted to obtain a prepolymer, and theobtained prepolymer is then subjected to a solid-state polymerizationunder reduced pressure, under an inert gas flow or under both reducedpressure and an inert gas flow, using a solid-state polymerizer.

With respect to materials for constructing these polymerizers used inthe present invention, there is no particular limitation. However,stainless steel, nickel or glass is generally used as a material for atleast inner wall portions of polymerizers.

With respect to the various types of reactors or polymerizers mentionedabove, especially a free-fall polymerizer having a perforated plate anda wire-wetting fall polymerizer having a perforated plate and at leastone wire, reference can be made, for example, to EP-0 738 743 A1.

In the method of the present invention, any of the above-mentionedtransesterification reaction modes can be used as long as thetransesterification is performed under the reaction conditions definedabove.

The reaction temperature of the transesterification for producing apolycarbonate is generally in the range of from 50 to 350° C.,preferably from 100 to 300° C. It is well known that when the reactiontemperature is higher than the above-mentioned range, the producedpolycarbonate is likely to suffer serious discoloration and tends tohave poor thermal stability, and that when the reaction temperature islower than the above-mentioned range, the polymerization proceeds soslowly that such a low temperature cannot be practically employed.

In the method of the present invention for producing a polycarbonate, asmentioned above, it is required that, in a stepwise transesterificationreaction of a polymerizable material, the relationship between thetemperature of and the residence time of the polymerizable material inthe reaction zones of the reaction system be controlled so as to satisfythe following formula (4): $\begin{matrix}{0.2 \leqq {\sum\limits_{i = 1}^{n}\quad \left( {{ki} \times {Ti} \times {Hi}} \right)} \leqq 1.2} & (4)\end{matrix}$

wherein:

i represents the zone number assigned in an arbitrary order among nreaction zones of the reaction system,

Ti represents the average temperature (° C.) of the polymerizablematerial in the i-th reaction zone,

Hi represents the average residence time (hr) of the polymerizablematerial in the i-th reaction zone,

ki represents a coefficient represented by the following formula (5):

ki=1/(a×Ti^(-b))   (5)

wherein Ti is as defined above, and

a and b depend on Ti, and wherein:

when Ti satisfies the formula:

Ti<240° C.,

a is 1.60046×10⁵ and b is 0.472,

when Ti satisfies the formula:

240° C.≦Ti<260° C.,

a is 4×10⁴⁹ and b is 19.107, and

when Ti satisfies the formula:

260° C.≦Ti,

a is 1×10¹²² and b is 49.082.

When the value of $\sum\limits_{i = 1}^{n}\quad$

(ki×Ti×Hi) in formula (4), which is determined by the relationshipbetween the above-mentioned temperature and residence time, is greaterthan 1.2, the produced polycarbonate has a disadvantage in that themechanical properties of the polycarbonate, such as elongation at breakand Izod impact strength, become poor. When the value of$\sum\limits_{i = 1}^{n}\quad$

(ki×Ti×Hi) is smaller than 0.2, the produced polycarbonate shows adisadvantage in that the molding melt fluidity of the polycarbonate ispoor. The preferred range of the value of$\sum\limits_{i = 1}^{n}\quad$

(ki×Ti×Hi) is from 0.3 to 1.0.

Generally, in a process for continuously producing a polycarbonate bytransesterification reaction, the transesterification reaction of thepolymerizable material is stepwise conducted in a plurality of reactionzones, wherein the reaction temperature, residence time and reactionpressure are stepwise changed over the plurality of reaction zonesinvolved in the process. The value of $\sum\limits_{i = 1}^{n}\quad$

(ki×Ti×Hi) in the formula (4) represents the sum of the values of(k×T×H) for all of the reaction zones. For example, when a continuouspolymerization is performed by using a system in which a vessel formelting and mixing an aromatic dihydroxy compound and a carbonicdiester, an agitation type reactor vessel, a centrifugal wiped filmevaporation type reactor and a surface renewal type twin screw kneadingreactor are serially connected through conduits,$\sum\limits_{i = 1}^{n}\quad$

(ki×Ti×Hi) is the sum of (k×T×H in the melting and mixing vessel),(k×T×H in the conduit connecting the melting and mixing vessel to theagitation type reactor vessel), (k×T×H in the agitation type reactionvessel), (k×T×H in the conduit connecting the agitation type reactorvessel to the centrifugal wiped film evaporation type reactor), (k×T×Hin the centrifugal wiped film evaporation type reactor), (k×T×H in theconduit connecting the centrifugal wiped film evaporation type reactorto the surface renewal type twin screw kneading reactor), (k×T×H in thesurface renewal type twin screw kneading reactor) and (k×T×H in theconduit connecting the surface renewal type twin screw kneading reactorto a nozzle for withdrawal of the produced polymer), that is, the sum ofvalues of (k×T×H) for all of the reaction zones including the conduits.The term “i-th reaction zone” means a reaction zone falling on thenumber i which is determined by the numbering system in which allreaction zones including conduits, such as a mixing vessel, a reactor ora conduit which connect these apparatuses, are assigned their respectivenumbers in the arbitrary order. When a heater is disposed on a conduitconnecting two reactors to each other, the conduit segment between oneof the reactors to the heater, the heater, and the conduit segmentbetween the heater and the other reactor are each regarded as a reactionzone. The average temperature of the polymerizable material means theaverage temperature of the polymerizable material in the i-th reactionzone. When the polymerizable material in the i-th reaction zone has atemperature distribution wherein different portions have distinctlydifferent temperatures, each of such different portions may beseparately regarded as an i-th reaction zone. With respect to themeasurement of the average temperature, various methods may be employed.For example, the average temperature can be obtained by averaging one ormore temperatures measured by one or more thermometers disposed at areactor or a conduit. When no thermometers are disposed at a reactor ora conduit, the temperature of a heating medium in a jacket may be usedas the average temperature. Alternatively, the average temperature ofthe inlet and outlet of a jacket for circulating a heating medium, orthe temperature which has been set for a heater or a heating medium maybe employed as the average temperature of the polymerizable material inthe i-th reaction zone. The average residence time is calculated bydividing the volume of the polymerizable material held in the i-threaction zone by the volume of the polymerizable material passingthrough or withdrawn from the i-th reaction zone per unit time.

A suitable reaction pressure is selected depending on the molecularweight of the polycarbonate in the reaction system. When the numberaverage molecular weight of the polycarbonate in the reaction system isless than 1,000, a reaction pressure in the range of from 50 mmHg toatmospheric pressure is generally employed. When the number averagemolecular weight of the polycarbonate in the reaction system is in therange of from 1,000 to 2,000, a reaction pressure in the range of from 3mmHg to 80 mmHg is generally employed. When the number average molecularweight of the polycarbonate in the reaction system is more than 2,000, areaction pressure of 10 mmHg or less, preferably 5 mmHg or less isgenerally employed.

A transesterification reaction can be carried out in the absence of acatalyst. However, if it is desired to accelerate the polymerization,the polymerization can be effected in the presence of a catalyst. Thepolymerization catalysts which are customarily used in the art can beused without particular limitation. Examples of such catalysts includehydroxides of an alkali metal and of an alkaline earth metal, such aslithium hydroxide, sodium hydroxide, potassium hydroxide and calciumhydroxide; alkali metal salts of, alkaline earth metal salts of andquaternary ammonium salts of boron hydride and of aluminum hydride, suchas lithium aluminum hydride, sodium boron hydride and tetramethylammonium boron hydride; hydrides of an alkali metal and of an alkalineearth metal, such as lithium hydride, sodium hydride and calciumhydride; alkoxides of an alkali metal and of an alkaline earth metal,such as lithium methoxide, sodium ethoxide and calcium methoxide;aryloxides of an alkali metal and of an alkaline earth metal, such aslithium phenoxide, sodium phenoxide, magnesium phenoxide, LiO—Ar—OLiwherein Ar represents an arylene group, and NaO—Ar—ONa wherein Ar is asdefined above; organic acid salts of an alkali metal and of an alkalineearth metal, such as lithium acetate, calcium acetate and sodiumbenzoate; zinc compounds, such as zinc oxide, zinc acetate and zincphenoxide; boron compounds, such as boron oxide, boric acid, sodiumborate, trimethyl borate, tributyl borate, triphenyl borate, ammoniumborates represented by the formula: (R¹ R² R³ R⁴)NB(R¹ R² R³ R⁴), andphosphonium borates represented by the formula: (R¹ R² R³ R⁴)PB(R¹ R² R³R⁴), wherein R¹ R² R³ and R⁴ are as defined above; silicon compounds,such as silicon oxide, sodium silicate, tetraalkylsilicon,tetraarylsilicon and diphenyl-ethyl-ethoxysilicon; germanium compounds,such as germanium oxide, germanium tetrachloride, germanium ethoxide andgermanium phenoxide; tin compounds, such as tin oxide, dialkyltin oxide,dialkyltin carboxylate, tin acetate, tin compounds having an alkoxygroup or aryloxy group bonded to tin, such as ethyltin tributoxide, andorganotin compounds; lead compounds, such as lead oxide, lead acetate,lead carbonate, basic lead carbonate, and alkoxides and aryloxides oflead or organolead; onium compounds, such as a quaternary ammonium salt,a quaternary phosphonium salt and a quaternary arsonium salt; antimonycompounds, such as antimony oxide and antimony acetate; manganesecompounds, such as manganese acetate, manganese carbonate and manganeseborate; titanium compounds, such as titanium oxide and titaniumalkoxides and titanium aryloxide; and zirconium compounds, such aszirconium acetate, zirconium oxide, zirconium alkoxide, zirconiumaryloxide and zirconium acetylacetone.

The catalysts can be used individually or in combination. The amount ofthe catalysts used is generally in the range of from 10⁻⁸ to 1% byweight, preferably from 10⁻⁷ to 10⁻¹% by weight, based on the weight ofthe aromatic dihydroxy compound.

By virtue of the presence of a plurality of specific heterounits in aspecific amount, the polycarbonate of the present invention isadvantageous in that not only does it have high transparency andcolorlessness as well as high mechanical strength, but also it exhibitshigh non-Newtonian flow properties, so that it exhibits high moldingmelt fluidity. Therefore, the polycarbonate of the present invention canbe advantageously used in various application fields.

The polycarbonate of the present invention may contain additivesdepending on the use of the polycarbonate. Examples of additives includea thermal stabilizer, an antioxidant, a weathering stabilizer, a UVlight absorber, a mold release agent, a lubricant, an antistatic agent,a plasticizer, a resin other than a polycarbonate or a polymer such as arubber, a pigment, a dye, a filler, a reinforcing agent, and a flameretardant.

These additives may be mixed with the polycarbonate obtained in themolten state. Alternatively, the mixing of additives may be performed bya method in which the polycarbonate is first pelletized, the additivesare mixed with the pelletized polycarbonate and the resultant mixture isagain subjected to melt-kneading.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be further illustrated in more detailwith reference to the following Examples and Comparative Examples, whichshould not construed as limiting the scope of the present invention.

In the following Examples and Comparative Examples, various propertieswere measured and evaluated as follows.

(1) Measurement of the weight average molecular weight of apolycarbonate:

The weight average molecular weight of a polycarbonate was measured bygel permeation chromatography (GPC).

(2) Evaluation of the color of a polycarbonate:

The color of a polycarbonate was evaluated, using a test specimen havinga 3.2 mm thickness which was obtained by injection molding at 280° C.,in accordance with the CIELAB method (Commission Internationale de 1′Eclairage 1976 L*a*b* Diagram). The yellowness of the specimen wasexpressed in terms of the b*-value. (3) Measurement of the elongation atbreak of a polycarbonate:

The elongation at break of a polycarbonate was measured, using a testspecimen having a 3.2 mm thickness which was obtained by injectionmolding at 280° C., in accordance with ASTM D638.

(4) Measurement of the Izod impact strength of a polycarbonate:

The Izod impact strength (notched) of a polycarbonate was measured,using a test specimen having a 3.2 mm thickness which was obtained byinjection molding at 280° C., in accordance with ASTM D256.

(5) Evaluation of the molding melt fluidity of a polycarbonate:

As a yardstick of the fluidity at a high shear rate, the HMI (which is amelt flow rate under a load of 21.6 kg) at 280° C. was measured inaccordance with ASTM D1238.

(6) Determination of recurring unit (1), heterounit (A) and heterounit(B) in a polycarbonate:

55 mg of a polycarbonate was dissolved in 2 ml of tetrahydrofuran. Tothe resultant solution, 0.5 ml of 5 N solution of potassium hydroxide inmethanol was added, and the solution was stirred at room temperature for2 hours to completely hydrolyze the polycarbonate. The obtained mixturewas mixed with 0.3 ml of concentrated hydrochloric acid and then, wassubjected to reversed phase liquid chromatography.

The reversed phase liquid chromatography was performed, using a 991L UVdetector (manufactured and sold by Waters Corporation, U.S.A) andInertsil ODS-3 column (registered trade mark, manufactured and sold byGL Science Inc., Japan) at 25° C. A mixture of methanol and 0.1 weight %aqueous solution of phosphoric acid was used as an eluent, andmeasurement was carried out by gradient elution technique at a gradientsuch that the volume ratio [methanol/0.1 weight % aqueous solution ofphosphoric acid] is changed from 20/80 at the start to 100/0.

The absorbance at 300 nm was measured using the UV detector. Absorbancecoefficients for determining recurring unit (1), heterounit (A) andheterounit (B) were obtained by using standard compounds [as standardcompounds, hydroxy compounds having structures formed by hydrolysis ofrecurring unit (1′), heterounit (2′) and heterounit (3′) were used].

EXAMPLE 1

A polycarbonate was produced by melt transesterification in accordancewith a system as shown in FIG. 1. The system of FIG. 1 comprises firststage, second stage and third stage agitation polymerizations, and firststage, and second stage wire-wetting fall polymerizations.

The first stage agitation polymerization in first agitation typepolymerizer vessels 3A and 3B (each having a capacity of 100 liters andequipped with an agitator having agitating blades of anchor type) wasbatchwise conducted, whereas the second stage and third stage agitationpolymerizations in second and third agitation type polymerizer vessels3C and 3D (each having a capacity of 50 liters and equipped with anagitator having agitating blades of anchor type) were continuouslyconducted.

The first stage and second stage wire-wetting fall polymerizations infirst and second wire-wetting fall polymerizers 108A and 108B werecontinuously conducted. Each of the first and second wire-wetting fallpolymerizers is equipped with a perforated plate which has 50 holeshaving a diameter of 7.5 mm and arranged in a zigzag configuration. Ineach of the first and second wire-wetting fall polymerizers, 50 strandsof 1 mmφ SUS 316 L wires are hung vertically from the respective holesof the perforated plate to a reservoir portion at the bottom ofwire-wetting fall polymerizer 108 so that a polymerizable material willnot fall freely (not free-fall) but fall along and in contact with thewires (wire-wetting fall). Illustratively stated, each wire 103 issecured at the upper end thereof to a support rod (not shown) providedabove the perforated plate 102 and extends downwardly through a hole(not shown) of the perforated plate 102. In each of the first and secondwire-wetting fall polymerizers, the wire-wetting fall distance is 8 m.

The polymerization reaction conditions in both of first agitation typepolymerizer vessels 3A and 3B were as follows: the reaction temperaturewas 180° C., the reaction pressure was atmospheric pressure, and theflow rate of nitrogen gas was 1 liter/hr.

In operation, 80 kg of polymerizable materials [i.e., bisphenol A as anaromatic dihydroxy compound and diphenyl carbonate as a carbonic diester(the molar ratio of diphenyl carbonate to bisphenol A:1.04)] werecharged together with a disodium salt of bisphenol A as a catalyst (theamount of the disodium salt of bisphenol A in terms of the amount ofsodium atom: 25 ppb by weight, based on the weight of the bisphenol A asa polymerizable material) into first agitation type polymerizer vessel3A. The monomer mixture in polymerizer 3A was polymerized in a moltenstate for 4 hours while agitating, to obtain prepolymer 4A. Outlet 5Awas opened, and prepolymer 4A was fed to second agitation typepolymerizer vessel 3C, having a capacity of 50 liters, at a flow rate of5 kg/hr.

While feeding prepolymer 4A obtained in first agitation type polymerizervessel 3A to second agitation type polymerizer vessel 3C, firstagitation type polymerizer vessel 3B was operated to polymerize themonomer mixture of bisphenol A and diphenyl carbonate in the same manneras in the agitation polymerization in first agitation type polymerizervessel 3A, to obtain prepolymer 4B.

When first agitation type polymerizer vessel 3A became empty, outlet 5Aof polymerizer 3A was closed and, instead, outlet 5B of polymerizer 3Bwas opened, so that prepolymer 4B was fed from first agitation typepolymerizer vessel 3B to second agitation type polymerizer vessel 3C ata flow rate of 5 kg/hr. In this instance, the same polymerizablematerials and catalyst as mentioned above were charged into polymerizer3A. While feeding prepolymer 4B obtained in first agitation typepolymerizer vessel 3B to second agitation type polymerizer vessel 3C,polymerizer vessel 3A was operated, so that the monomer mixture chargedtherein was polymerized in the same manner as mentioned above.

With respect to a batchwise polymerization in first agitation typepolymerizer vessels 3A and 3B and the alternate feedings of prepolymers4A and 4B from polymerizers 3A and 3B to second agitation typepolymerizer vessel 3C, the same operation as mentioned above wasrepeated, so that the prepolymer (either prepolymer 4A or prepolymer 4B,alternately) was continuously fed to second agitation type polymerizervessel 3C.

In second agitation type polymerizer vessel 3C, a further agitationpolymerization of prepolymers 4A and 4B, alternately fed from firstagitation type polymerizer vessels 3A and 3B, was continuously carriedout under polymerization reaction conditions wherein the reactiontemperature was 230° C., the reaction pressure was 100 mmHg and the flowrate of nitrogen gas was 2 liters/hr, thereby obtaining prepolymer 4C.

When the volume of prepolymer 4C in second agitation type polymerizervessel 3C reached 20 liters, a part of prepolymer 4C was continuouslyfed to third agitation type polymerizer vessel 3D so that the volume ofprepolymer 4C in second agitation type polymerizer vessel 3C wasconstantly maintained at 20 liters.

In third agitation type polymerizer vessel 3D, a further agitationpolymerization of prepolymer 4C fed from second agitation typepolymerizer vessel 3C was continuously carried out under polymerizationreaction conditions wherein the reaction temperature was 240° C., thereaction pressure was 10 mmHg and the flow rate of nitrogen gas was 2liters/hr, thereby obtaining prepolymer 4D.

When the volume of prepolymer 4D in third agitation type polymerizervessel 3D reached 20 liters, a part of prepolymer 4D was continuouslyfed to wirewetting fall polymerizer 108A so that the volume ofprepolymer 4D in second agitation type polymerizer vessel 3D wasconstantly maintained at 20 liters. The feeding of prepolymer 4D tofirst wire-wetting fall polymerizer 108A was conducted through inlet101A.

In first wire-wetting fall polymerizer 108A, a wire-wetting fallpolymerization of prepolymer 4C was continuously carried out underpolymerization reaction conditions wherein the reaction temperature was245° C., and the reaction pressure was 1.5 mmHg and the flow rate ofnitrogen gas was 4 liter/hr, thereby obtaining prepolymer 109A.

When the volume of prepolymer 109A at the bottom of first wire-wettingfall polymerizer 108A reached 10 liters, a part of prepolymer 109A wascontinuously fed to second wire-wetting fall polymerizer 108B so thatthe volume of prepolymer 109A in first wire-wetting fall polymerizer108A was constantly maintained at 10 liters.

In second wire-wetting fall polymerizer 108B, a wire-wetting fallpolymerization reaction was continuously carried out underpolymerization reaction conditions wherein the reaction temperature was245° C., and the reaction pressure was 0.3 mmHg and the flow rate ofnitrogen gas was 2 liter/hr, thereby obtaining polycarbonate 109B.

When the volume of polycarbonate 109B at the bottom of secondwire-wetting fall polymerizer 108B reached 10 liters, polycarbonate 109Bwas continuously withdrawn in the form of a strand from secondwire-wetting fall polymerizer 108B through outlet 107B by means ofdischarge pump 106B so that the volume of polycarbonate 109B in secondwire-wetting fall polymerizer 108B was constantly maintained at 10liters. The obtained strand was cut into pellets by means of a strandcutter.

The temperature, the residence time and the value of (Ki×Ti×Hi) in eachof the agitation type polymerizer vessels, in each of the wire-wettingfall polymerizers and in each of the conduits are shown in Table 1,together with the value of$\sum\limits_{i = 1}^{n}{\left( {K\quad i \times T\quad i \times H\quad i} \right).}$

(Ki×Ti×Hi). with respect to the obtained polycarbonate pellets,evaluation of various properties was made in accordance with theabove-mentioned methods. Results are shown in Table 2. As can be seenfrom Table 2, the obtained polycarbonate had excellent properties.

Further, as a result of the measurement by reversed phase liquidchromatography, it was found that the obtained polycarbonate containedunits of formula (2′)-(a) as heterounit (A) and units of formula(3′)-(d) as heterounit (B), wherein the units of formula (3′)-(d) werepresent in an amount of 0.50 mole %, based on the molar amount of theunits of formula (2′)-(a), and wherein the sum of the amounts of theunits of formula (2′)-(a) and the units of formula (3′)-(d) was 0.09mole %, based on the molar amount of recurring units (1).

COMPARATIVE EXAMPLE 1

A polycarbonate was produced in substantially the same manner as inExample 1, except that the temperatures in some of the reaction zoneswere changed as shown in Table 3.

With respect to the obtained polycarbonate, evaluation of variousproperties was made in accordance with the above-mentioned methods.Results are shown in Table 2. As can be seen from Table 2, the obtainedpolycarbonate had excellent molding melt fluidity; however, the color,tensile elongation and Izod impact strength of the obtainedpolycarbonate were poor.

COMPARATIVE EXAMPLE 2

A polycarbonate was produced in substantially the same manner as inExample 1, except that a centrifugal wiped film evaporation type reactorand a horizontal twin-screw agitation type polymerizer were used insteadof first wire-wetting fall polymerizer 108A and second wire-wetting fallpolymerizer 108B, respectively, and that the reaction conditions werechanged as shown in Table 4.

With respect to the obtained polycarbonate, evaluation of variousproperties was made in accordance with the above-mentioned methods.Results are shown in Table 2. As can be seen from Table 2, the obtainedpolycarbonate had excellent molding melt fluidity; however, the color,tensile elongation and Izod impact strength of the obtainedpolycarbonate were poor.

COMPARATIVE EXAMPLE 3

With respect to a commercially available phosgene process polycarbonate(the Mw of the polycarbonate: 26,800), evaluation of various propertieswas made in accordance with the above-mentioned method. Results areshown in Table 2. Although the poycarbonate used in this ComparativeExample had the same Mw as that of the polycarbonate obtained in Example1, the polycarbonate of this Comprarative Example had poor molding meltfluidity, as compared to the polycarbonate of Example 1.

EXAMPLE 2

A polycarbonate was produced in substantially the same manner as inExample 1, except that the reaction conditions were changed as shown inTable 5.

With respect to the obtained polycarbonate, evaluation of variousproperties was made in accordance with the above-mentioned methods.Results are shown in Table 2. As can be seen from Table 1, the obtainedpolycarbonate had excellent properties.

TABLE 1 [Reaction Conditions in Example 1] Temperature Residence time$\sum\limits_{i = 1}^{n}\left( {{ki} \times {Ti} \times {Hi}} \right)$

Reaction zones (° C.) (hr) (ki × Ti × Hi) in the process of Example 1First agitation 180 20.0  0.261 0.83 type polymerizer vessels 3A, 3BConduit 180 0.6 0.008 Second agitation 230 7.2 0.135 type polymerizervessel 3C Conduit 230 0.2 0.004 Third agitation 240 8.3 0.150 typepolymerizer vessel 3D Conduit 240 1.6 0.029 First wire- 245 4.3 0.117wetting fall polymerizer 108A Conduit 245 0.1 0.003 Second wire- 245 4.40.119 wetting fall polymerizer 108B Conduit 245 0.2 0.005 Note: In eachof Tables 1, 3, 4 and 5, each “conduit” item between the polymerizeritems shows the reaction conditions in a conduit between a polymerizermentioned above the “conduit” item and a polymerizer mentioned below the“conduit” item, and the “conduit” item at the lowermost row shows thereaction conditions in a conduit between the last polymerizer (for afinal product) and a withdrawal nozzle.

TABLE 2 Compar- Compar- Compar- Evaluation ative ative ative itemsExample 1 Example 1 Example 2 Example 3 Example 2 Molar ratio 0.09 0.460.69 0.00 0.16 (%) of the total of heterounits (A) and (B) to the totalof recurring units (1) Molar ratio 0.30 33.00 42.00 — 2.30 (%) of hete-rounits (B) to heterounits (A) Weight 26,800 26,900 27,000 26,800 26,900average molecular weight Molding 145 166 179 118 153 melt fluidity, HMI(g/10 min) Color (b* 3.2 4.3 5.0 3.2 3.4 value) Tensile 107 78 69 107102 elongation (%) Izod impact 98 83 81 98 96 strength (kg · cm/ cm)

TABLE 3 [Reaction Conditions in Comparative Example 1]$\sum\limits_{i = 1}^{n}\left( {{ki} \times {Ti} \times {Hi}} \right)$

Temperature Residence time in the process of Reaction zones (° C.) (hr)(ki × Ti × Hi) Comparative Example 1 First agitation 180 20.0  0.2613.87 type polymerizer vessels 3A, 3B Conduit 180 0.6 0.008 Secondagitation 230 7.2 0.135 type polymerizer vessel 3C Conduit 230 0.2 0.004Third agitation 250 8.3 0.342 type polymerizer vessel 3D Conduit 250 1.60.065 First wire- 260 4.3 0.378 wetting fall polymerizer 108A Conduit260 0.1 0.009 Second wire- 270 4.4 2.547 wetting fall polymerizer 108BConduit 270 0.2 0.117

TABLE 4 [Reaction Conditions in Comparative Example 2]$\sum\limits_{i = 1}^{n}\left( {{ki} \times {Ti} \times {Hi}} \right)$

Temperature Residence time in the process of Reaction zones (° C.) (hr)(ki × Ti × Hi) Comparative Example 2 First agitation 140 20.0  0.18015.52 type polymerizer vessels 3A, 3B Conduit 140 0.6 0.005 Secondagitation 210 7.2 0.118 type polymerizer vessel 3C Conduit 210 0.2 0.004Third agitation 240 8.3 0.150 type polymerizer vessel 3D Conduit 240 1.60.029 Centrifugal 270 0.5 0.293 wiped film evaporation type reactorConduit 270 0.1 0.059 Horizontal 290 0.5 10.490  twin-screw agitationtype polymerizer Conduit 290 0.2 4.196

TABLE 5 [Reaction Conditions in Example 2] Temperature Residence time$\sum\limits_{i = 1}^{n}\left( {{ki} \times {Ti} \times {Hi}} \right)$

Reaction zones (° C.) (hr) (ki × Ti × Hi) in the process of Example 2First agitation 140 20.0  0.180 0.97 type polymerizer vessels 3A, 3BConduit 160 0.6 0.007 Second agitation 210 3.6 0.059 type polymerizervessel 3C Conduit 210 0.2 0.004 Third agitation 240 4.1 0.074 typepolymerizer vessel 3D Conduit 240 1.6 0.029 First wire- 245 2.2 0.060wetting fall polymerizer 108A Conduit 250 0.1 0.004 Second wire- 265 2.20.505 wetting fall polymerizer 108B Conduit 265 0.2 0.046

INDUSTRIAL APPLICABILITY

By virtue of the presence of specific heterounits in a specific amountin the polycarbonate main chains, the polycarbonate of the presentinvention is advantageous in that not only does it have hightransparency and colorlessness as well as high mechanical strength, butalso it can exhibit extremely high molding melt fluidity. Therefore, thepolycarbonate of the present invention can be used in a wide variety ofapplication fields.

We claim:
 1. A polycarbonate comprising a plurality of aromaticpolycarbonate main chains, each comprising recurring units eachindependently represented by the following formula (1):

wherein Ar represents a divalent C₅-C₂₀₀ aromatic group, wherein atleast one of said aromatic polycarbonate main chains contains , whenconsidered together as a whole, contain therein at least one heterounit(A) and at least one heterounit (B) in said polycarbonate main chains ,said heterounit (A) being represented by at least one formula selectedfrom the group consisting of formulae of the following group (2):

wherein Ar′ represents a trivalent C₅-C₂₀₀ aromatic group, Ar″represents a tetravalent C₅-C₂₀₀ aromatic group, and X represents apolycarbonate chain having recurring units each represented by theformula

wherein Ar is as defined above and having a weight average molecularweight of from 214 to 100,000, and wherein, when said polycarbonate mainchains contain a plurality of heterounits (A), the heterounits (A) arethe same or different, said heterounit (B) being represented by at leastone formula selected from the group consisting of formulae of thefollowing group (3):

wherein Ar, Ar′ and X are as defined above and Y represents apolycarbonate chain having recurring units each represented by theformula

wherein Ar is as defined above and having a weight average molecularweight of from 214 to 100,000, and wherein, when said polycarbonate mainchains contain a plurality of heterounits (B), the heterounits (B) arethe same or different, the sum of the amounts of said heterounit (A) andsaid heterounit (B) being from 0.01 to 0.3 mole %, based on the molaramount of said recurring units (1), wherein each of said X and said Yoptionally contains at least one heterounit selected from the groupconsisting of heterounits (A) and (B), said polycarbonate having aweight average molecular weight of from 5,000 to 300,000.
 2. Thepolycarbonate according to claim 1, wherein 85% or more of saidrecurring units (1) are each represented by the following formula (1′):


3. The polycarbonate according to claim 1, wherein: said recurring units(1) are each represented by the following formula (1′):

said heterounit (A) is represented by at least one formula selected fromthe group consisting of formulae of the following group (2′):

wherein X is as defined for formula (2), and said heterounit (B) isrepresented by at least one formula selected from the group consistingof formulae of the following group (3′):

wherein X is as defined for formula (2), and Y is as defined for formula(3).
 4. The polycarbonate according to any one of claims 1 to 3, whereinsaid heterounit (B) is present in an amount of from 0.1 to 30 mole %,based on the molar amount of said heterounit (A).
 5. The polycarbonateaccording to any one of claims 1 to 3, which is produced from anaromatic dihydroxy compound and a carbonic diester bytransesterification.
 6. In a method for producing a polycarbonate whichcomprises subjecting to a stepwise transesterification reaction, in aplurality of reaction zones, at least one polymerizable materialselected from the group consisting of: a molten monomer mixture of anaromatic dihydroxy compound and a carbonic diester, and a moltenprepolymer obtained by a process comprising reacting an aromaticdihydroxy compound with a carbonic diester, said aromatic dihydroxycompound being represented by the following formula: HO—Ar—OH wherein Arrepresents a divalent C₅-C₂₀₀ aromatic group, said carbonic diesterbeing represented by the following formula:

wherein Ar³ and Ar⁴ are the same or different and each represent amonovalent C₅-C₂₀₀ aromatic group, the improvement in which saidstepwise transesterification reaction of the polymerizable material isperformed under reaction conditions which satisfy the following formula(4):$0.2 \leq {\sum\limits_{i = 1}^{n}\quad \left( {{ki} \times {Ti} \times {Hi}} \right)} \leq 1.2$

wherein: i represents the zone number among n reaction zones of thereaction system, Ti represents the average temperature (°C.) of thepolymerizable material in the i-th reaction zone, Hi represents theaverage residence time (hr) of the polymerizable material in the i-threaction zone, ki represents a coefficient represented by the followingformula (5): ki=1/(a×Ti^(-b))   (5) wherein Ti is as defined above, anda and b depend on Ti, and wherein: when Ti satisfies the formula:Ti<240° C., a is 1.60046×10⁵ and b is 0.472, when Ti satisfies theformula: 240° C.≦Ti<260° C., a is 4×10⁴⁹ and b is 19.107, and when Tisatisfies the formula: 260° C.≦Ti, a is 1×10¹²² and b is 49.082.
 7. Apolycarbonate which is the same product as produced by the method ofclaim 6.